Study On The Effects Of Nitrogen Management On Ammonia Volatilization And Nitrogen Leaching In Citrus Orchard

In recent years,with the rapid development of citrus industry,citrus has become the largest fruit crop in the world and the fruit tree with the widest planting area in Southwest China.However,the problem of excessive nitrogen application in the process of citrus planting in China is prominent.Under the climatic characteristics of abundant rainfall and the same season of rain and heat,the nitrogen loss in the main citrus producing areas in Southwest China is more serious,resulting in a series of problems such as low nitrogen use efficiency,resource waste and environmental pollution,which seriously restricts the sustainable development of citrus industry.Therefore,quantifying the annual loss characteristics of active nitrogen in typical citrus orchards and establishing scientific and reasonable nitrogen control measures is an important problem to be solved in citrus green production in China.Therefore,this study established six field in-situ experiments of nitrogen application rates of N₀（0 kg N/ha）,N₄₈（48 kg N/ha）,N₉₆（96 kg N/ha）,N₁₄₄（144kg N/ha）,N₂₁₆（216 kg N/ha）and N₃₀₀（300 kg N/ha）,and established large-scale leakage device experiments with different nitrogen application rates（the same as the field experiment）and different organic substitution ratios（0,25%,50%,75%and 100%,based on the optimized nitrogen application rate）,The characteristics of annual ammonia volatilization and nitrogen leaching loss in citrus orchards were quantitatively studied,and the effects of the above measures on soil nitrogen residue,tree nitrogen uptake,citrus yield and quality were discussed.The appropriate nitrogen regulation scheme was preliminarily put forward,in order to provide theoretical support for the optimal nitrogen fertilization management of citrus orchards in Southwest China.The main results are as follows:（1）The field experiment results of different nitrogen application rates showed that summer was the peak period of ammonia volatilization,and the ammonia volatilization rate and loss increased with the increase of nitrogen application rate.The annual total amount of ammonia volatilization of each nitrogen application treatment was 6.78-52.5 kg N/ha,and the annual ammonia volatilization factor was9.07%-16.7%;Compared with farmers’customary nitrogen application(N₃₀₀),other nitrogen application treatments reduced ammonia volatilization loss by 34.8%-87.1%.Nitrogen leaching mainly occurs in rainy season（July-September）,and nitrate nitrogen is the main form of nitrogen leaching;The amount of nitrogen leaching was positively correlated with the amount of nitrogen application.The annual leaching amount of total nitrogen（TN）in each nitrogen application treatment was 131-217 kg N/ha,accounting for33.8%-36.7%of the amount of nitrogen application.Among them,the loss rate of optimized nitrogen application(N₁₄₄)was the lowest,which was 25.6%less than that of farmers’customary nitrogen application(N₃₀₀).The content and residue of soil inorganic nitrogen were positively correlated with the amount of nitrogen application.In the 0-80 cm soil layer,the residue of each nitrogen application treatment was 91.2-174 kg N/ha,accounting for 26.8%-32.5%of the amount of nitrogen application.Proper nitrogen application can promote the growth and nitrogen accumulation of citrus branches,increase the content and accumulation of fruit nutrients,single fruit weight and yield,and improve the fruit quality（TSS,Vc,total sugar and TSS/TA）.When the amount of nitrogen fertilizer is 144 kg/ha,the fruit nutrient uptake and yield are the highest,the fruit quality is the best,and the nitrogen use efficiency is the highest.The fate of fertilizer nitrogen in citrus orchard is mainly nitrogen leaching and soil residue.The optimal application of nitrogen(N₁₄₄)in each treatment can significantly reduce nitrogen loss and improve nitrogen use efficiency.（2）Under the condition of large-scale pot culture and fertigation,the ammonia volatilization rate increased exponentially with the increase of nitrogen application,and the peak of ammonia volatilization was in August in summer;The annual ammonia volatilization total amount of each nitrogen application treatment is 3.44-42.8 kg N/ha,and the annual ammonia volatilization factor is 1.51%-13.4%;Compared with farmers’customary nitrogen application(N₃₀₀),the ammonia volatilization reduction rate of other nitrogen application treatments is 55.8%-92.0%.In the large-scale pot experiment,nitrogen leaching loss mainly occurred in the rainfall concentration period from July to September,and nitrate nitrogen was the main form of nitrogen leaching;The annual leaching amount of TN in each nitrogen application treatment was 141-212 kg N/ha,and the loss rate was 25.1%-29.8%;The loss rate of optimized nitrogen application(N₁₄₄)was the lowest,which reduced the nitrogen leaching loss by 22.3%compared with the treatment of farmers.In the 0-30 cm soil layer,the content and residue of inorganic nitrogen increased with the increase of nitrogen application.The residue of each nitrogen application treatment was 31.5-77.5 kg N/ha,accounting for 15.3%-23.0%of the nitrogen application.Nitrogen application promoted the growth of citrus branches and shoots and nitrogen accumulation.With the increase of nitrogen application,the agronomic properties of trees,dry matter of branches and shoots,nitrogen content and accumulation increased in varying degrees.When the amount of nitrogen application was 144 kg/ha,the nitrogen use efficiency was the highest.In the fate of fertilizer nitrogen,other ways（deep soil nitrogen residue and denitrification gas,etc.）accounted for the highest proportion,followed by nitrogen leaching and soil residue;In each treatment,the optimal nitrogen application(N₁₄₄)had the least nitrogen leaching loss rate,and the highest proportion of soil residue and plant absorption.（3）The results showed that the ammonia volatilization rate was negatively correlated with the organic substitution ratio,and the ammonia volatilization peak was in August in summer;The annual ammonia volatilization total amount of each treatment is between 3.43-6.89 kg N/ha,and the annual ammonia volatilization factor is 0.41%-2.90%;Compared with pure fertilizer nitrogen（NPK）,the emission reduction rate of ammonia volatilization in different organic substitution ratios is 17.9%-51.9%.The leaching loss of nitrogen under the fertigation mainly occurred in the rainy season（July-September）,with nitrate nitrogen as the main leaching form;Nitrogen leaching loss was negatively correlated with the proportion of organic substitution.The annual leaching amount of TN in each treatment was 144-165 kg N/ha,and the loss rate was 10.7%-25.1%;Compared with pure fertilizer nitrogen,organic substitution reduced nitrogen leaching by 3.18%-12.6%.In the 0-30 cm soil layer,the nitrogen residue of each treatment is 47.9-64.6 kg N/ha.With the increase of the application proportion of organic fertilizer,the inorganic nitrogen residue decreases,but the content of soil total nitrogen and organic matter increases significantly,enhances the soil nitrogen supply capacity and reduces the loss of active nitrogen.Under the fertigation,the substitution of organic fertilizer for 50%chemical fertilizer nitrogen significantly promoted the increase of tree agronomic characters,autumn shoot nitrogen content and accumulation,and improved nitrogen use efficiency.Under the fertigation,other ways（including soil organic nitrogen form,deeper soil nitrogen residue,denitrification gas loss,etc.）account for the highest proportion and ammonia volatilization loss accounts for the lowest proportion.In each treatment,organic fertilizer instead of 50%chemical fertilizer nitrogen can effectively reduce the loss of fertilizer nitrogen,improve the nitrogen utilization rate of citrus,and increase soil fertility and nitrogen supply capacity.In conclusion,under the two fertilization methods,the optimized nitrogen application(N₁₄₄)showed good emission reduction effect,and was conducive to the uptake and utilization of nitrogen in citrus;Under the fertigation,compared with the pure application of chemical fertilizer nitrogen,the substitution of organic fertilizer for 50%of chemical fertilizer nitrogen effectively reduces the loss of ammonia volatilization and nitrogen leaching,better promotes the growth of citrus,improves the use efficiency of nitrogen fertilizer,and fertilizes the soil.It is a scientific fertilization method to realize the green and sustainable development of citrus with improved quality and efficiency and environment-friendly.